Thanks, that was my favorite part of android. I do use Textra but I prefer a text app w themes. I read the article, didn't understand any of it.

Haha, it's OK. Basically it says that a (limited) themeing engine is in the code on O previews, but it's not active, so it will likely not make it 'live' when the final version rolls out. But even if it did, it will be a limited resource. For full-on themeing, you would need to root or have the app support custom notification icons.